Electrical sound-producing apparatus



Feb. 28, 1928. 7 1,660,321

- T- BODDE ELECTRICAL SOUND PRODUCING APPARATUS Original Filed Aug. 1,1923 MILLI- AMPERES GAUSSS INVENTOR Theodore Bocld e BY A ATTORNEY v.

coil surrounding .current pulsations or impulses by .into correspondingPatented Feb. 28, 1928.

THEODORE BODDE, OF LEWISTON, NEW YORK.

ELECTRICAL SOUND-PRODUCING- APPARATUS.

Application filed August 1, 1923,

This invention relates to an apparatus for electrically producing sound,and more particularly to an apparatus for transforming sound waves orimpulses into corresponding the action of an electron discharge tube orvalve; and has special reference to an improved apparatus of the naturedisclosed in my copending application Serial No. 613,273, filed Jan. 17,1923.

As described in my said copending application, it is known that theelectron stream or current between the electrodes of a vacuum tube orelectron discharge valve maybe controlled by means of a magnetic field.In the action of these magnetically controlled valves if a constantvoltage is impressed between the cathode and anode, the current thatflows through the tube, that is, the electron stream that dischargesfrom the cathode and impinges on the anode, while unaffected by amagnetic field having a strength less than a critical value, is reducedto zero if the magnetic field is increased beyond that value; and thusby changing the strength of the magnetic field to magnitudes below orabove a critical amount, the current across the electrodes and hence thecurrent in a Working circuit connected to the electrodes may berespectively established or extinguished. I have discovered that thisphenomenon or property of magnetic control of the electron emission ofthe tube or valve may be utilized for effecting the transformation ofsound vibrations or impulses electrical impulses for sound productionand transmission; and that the tube or valve may be so constructedordesigned as to permit of accomplishing this result. p

The magnetically controlled electron tube, or magnetron as it is termed,in one of its most efiicient forms comprises a vacuous vessel ofcylindrical configuration provided with an axially disposed filamentwhich when heated to incandescence emits an electron stream whichimpinges upon a cylindrical plateor anode symmetric-ally surrounding thecathode, the stream being controlled'by means of a magnetic fieldpreferably produced by an energized-solenoid or the tube Or vessel. Thepaths of movement of the electron projected from the cathode are foundto be influenced by the magnetic field, the paths being bent Serial No.655,005. Renewed April 21, 1927.

or curved by. the magnetic field,-the degree of curvature imparted tothe paths var ing with the strength of the magnetic eld When themagnetic field is below a critical value, the electron paths althoughcurved still intersect the cylindrical anode, and since the electronsimpinge on the electrons the anode, :the current through the tuberemains unaffield of electrons bei-'.g then less than the radius of thecylindrical anode, electrons do not impinge on the anode, no currentflows across the electrodes and the i and since the current in theworking circuit is accordingly extingulshed.

When the parts ruptly changed rom the maximum to zero of the magnetronare symmetrlcally arran ed, the" current may beab-.

value, the transition from a closed to an open circuit bein however notabrupt where there isa lack 0 symmetry. I have discov-- ered that whenthe magnetron is subjected" to mechanical vibrations, a relativevibration between the cathode and the anode is roduced, the cathode orfilament, due to its inertia, remaining suspended in space sta' tionarywith respect to the vibrating anode, and as a result not only "isadis-symmetry produced which changes or variations in the electronstream when the magnetic field is at or about the critical point, butwhen the magnetron construction is modified as will appear hereinpermitsof more gradualafter, variations in the current in the work- I mgcircuit are obtainablecorresponding 1n magnitude and frequency to thevibrations to which the tube is subjected, the magnetron being'thusrendered serviceable and adaptable for translating sound vibrations intosound producing electrical pulsations.

As heretofore mentioned, the electron stream is controlled. by a certaincritical value of the magnetic field voltage is impressed upon themagnetron electrodes.- It. is known "that the critical value of a givenmagnetron varies with and proportional to the square root of the voltageimpressed upon the electrodes. foundthat in the operation of the soundproducing apparatus variationstake place in the working circuit thereof,which variations produce "changes in the voltage im- .100 if a constante pressed upon the magnetron electrodes especially When said workingcircuit possesses high inductance and resistance factors, and in orderto produce a pure and strongiconversion of the mechanical vibrationsinto electrical impulses, it is highly desirable to compensate for thechanges in the impressed voltage. It is accordingly a principal objectof my present invention to provide an improved sound producing apparatusof this nature in which the voltage variations or fluctuations arecompensated for so that the activit of the apparatus is made independentof changes in the critical value of the magnetron.

To the accomplishment of the foregoing and such other objects as mayhereinafter appear, my invention consists in the elements and theirrelation one to the other, as hereinafter particularly described andsought to be defined in the claims, reference bein had to theaccompanying drawings whie show referred embodiments of my invention,and in which:

Fig. 1 is a view showing my invention applied to a transmitter,

Fig. 2 is a diagrammatic view of a modification of my invention,

Fi 3 is a graphical view showing the electrica characteristics of themagnetron and the manner of adjusting the magnetic field thereof, Y

Figs. 4 and 5 are diagrammatic views depictingthe principles or theoryunderlying the invention, and

Fig. 6 is a modification of the construction of the magnetron devicewhich maybe employed.

Referring now more in detail to the drawings and more artieularly toFig. 1 thereof, the magnetical y control ed valve'or magnetron generallydesignated as M is shown to comprise a vacuous vessel or tube 10provided with the cathode in the form of a straight filament 11 arrangedaxiall of the tube, and an anode 12, the said ano e in the inventionhere exemplified comprising a sectionor portion of a surface of acylinder as will be detailed hereinafter, the filament being providedwith the sealed terminals 13 and 14 and the anodebeing provided with thesealed terminal 15; and encircling the tube 10 symmetricall with thecathode and anode there is provi ed the solenoid 16 for producing acontrolling magnetic field.

For heating the filament to incandescenee a closed circuit is provided.which includes the battery 17, the op osite poles of which are connectedto the lament terminals 13 and 14; by means of the conductors 18 and 19.As is well known, upon heating the filament 11 by means of-this closedcircuit, there will take place an emission of electrons from thefilament 11 to the anode 12, and upon closing a Working circuitconnected to the anodeand cathode a current will be establishedtherethrough.

For energizing the solenoid 16 the same may be connected to a source ofcurrent which may be the battery 17 by means of a circuit comprising theconductor 20, the coil of the solenoid 16, conductor 21, and rheostat22, the rheostat being employed for predetermining the degree ofenergization of the solenoid and hence the magnitude of the magneticfield thereof.

As above mentioned, it the electron tube be subjected to a magneticfield below a predetermined amount, the emission of electrons from thecathode and the impinging of these electrons on the anode of the tubewill be uninterrupted and unhindered, and that if the tube be subjectedto a magnetic field beyond such predetermined amount, the electrons willbe diverted and prevented from reaching the anode, resulting in anopening of the tube circuit and the opening of the working circuitcontrolled thereby. The graphical representation of this phenomenon isshown in Fig. 3, in which the strength of the magnetic field isrepresented by the abscissze, and the strength of the current flowingbetween the cathode and anode is represented by the ordinates of thegraph. If the magnetizing influence is less than the line represented asCD, the current in the workin circuit will be a maximum represented bythe line XC. If, however, the magnetization passes the point D, thecurrent in the Working circuit decreases and rapidly diminishes to aminimum as the magnetic field approaches the value XE, the chan e alongthe curve DE being more or less abrupt as the parts of the magnetron aremore or less symmetrical in arrangement.

For the purpose of transforming vibrations such as sound vibrations intocorresponding electrical pulsations, the magnetron of my presentinvention is mounted on a vibratable member which may be set intovibration in accordance with sound Waves impinging thereon, the saidvibratable member comprising for example a sounding board or a diaphragmof a transmitter. This is shown for example in Fig. 1 of the drawings,and referring to this figure, the magnetron is shown mounted formovement with a diaphragm 23 associated with the mouth-piece 24, themagnetron being referably bodily mounted on and carried y the diaphragm23 by means of the sup porting element 25. Also preferably in order tominimize the weight carried by the diaphragm 23, the tube 10 alone ismounted thereon, the solenoid 16 being arranged so as to be maintainedin a relatively stationary condition during vibration of the tube. Withthis construction as the diaphragm and the tube are set into vibratorymotion, the anode 12 is moved relatively to the cathode or filament 11,the latter remaining suspended in stationary position due to itsinertia. In order to heighten this inertia effect, the cathode 11 may beweighted at its ends as by means of the small weights 26, 26. When thetube isset into vibratory motion and when the solenoid 16 is energizedto produce a magnetic field at or about the critical value, the relativevibration between the anode and the cathode effects variations in theelectron stream reaching the anode, which variations are proportional inmagnitude or amplitude and frequency to the oscillations or vibrationsimpressed upon the tube. By connecting across the electrodes a receivingcircuit which may include the receiver 27, the transformer 28, thebattery 29 and conductors 30 and 31, it will be apparent that thevariations in the electron stream will produce corresponding soundproducing variations in the current of the working or receiving circuit.

That the change in the electric current or stream varies proportionallywith the impressed mechanical vibrations of the tube system will appearfrom a consideration of Figs. 3 to 5 of the drawings. In these figures Ihave attempted to depict in a diagrammatic fashion the underlying theoryof the invention, and I desire it to be understood' that although thistheory I believe to be properly explanatory of the phenomenon or thebehaviour of the apparatus, the theory is presented by way ofexplanation only, and not by way of limitation. When the magnetic fieldactive on the magnetron is of a magnitude equal to the critical value ofthe tube as represented for example by the asterisk on the curverepresented in Fig. 3, the current in the'tube is at the transitionpoint, and the average electron path may be represented by the curve a:(Fig. 4), the electron path being tangent to the anode 12. This,however, is only the average path, and due to such factors as thephysical dimension of the filament, the lack of complete symmetry of theparts, etc, the electrons are rojected from the cathode in a plurality oproximate paths such for'example as the paths :1), y and 2, theelectrons in the path a impinging on the anode, and the electrons in thepath y circling about in a closed path, as shown, without touching theanode. When the tube is vibrated, however, more or less of the electronsreach the anode according to the position of the tube and attached anodewith respect to the relatively stationary cathode. This is shown in Fig.5 of the drawings, wherein the diaphragm 23, tube 10 and anode 12 areshown in three successive positions F, G and H, the anode in position 12embracing the electron paths m, y and z, the anode position 12 embracingthe paths w and z, and the anode in position 12embracing only the anode,

path a. It will therefore be evident that the total electron streamemanating from the filament and impinging against the cylindrical anodesurface varies progressively with and in proportion to the vibratorymotion of the tube.

In the construction shown in Fig. 1 and diagrammatically indicated inFigs. 3 to 5, the anode 12 is a section or a part of a cylinder, andmore particularly a cylinder with one side cut away, and the preferredform comprises a quadrant of a cylinder. The cylindrical anode asdistinguished from the known ma-gnetrons is cut away on one side for thereason that if a full cylinder be employed any variation in the electroncurrent on one side produced by the vibrations would be neutralized byan equal and opposite variation on the opposite side, producing a netresult of no variations in the working circuit. With one side' of thehowever, removed, the electron stream variations on one side of thecylinder produce a current in the working circuit as desired. The sameresults may be accomplished by utilizing a complete cylindrical anode,however, and by eccentrically arranging the anode and cathode as will bedetailedfurther hereinafter.

As already mentioned, a desideratum of the present invention comprehendsthe provision of an improved sound producing apparatus in which thevoltage variations in the receiver circuit are compensated for so as torender the operation of the device independent of changes in thecritical value of the magnetron, directly proportional to the squareroot of the voltage between the cathode and the anode. To accomplish thedesired result, I provide means for producing variations in the magneticfield which controls the magnetron proportional to the changes in thecritical value of the magnetron due to the variations in the receivercircuit, and with such means I maintain substantially the same relativeproportion between the magnitude of the active or controlling magneticfield and the square root of the voltage effective across theelectrodes. The means I prefer to provide for effecting the desiredcompensation comprises a circuit including a magnetizing coil 32surrounding the mag netron tube to produce a magnetic field which iscombined with the magnetic field of the coil 16, both fields producing aresultant controlling field having a. magnitude which maintains themagnetron at its critical point, the said circuit further including theconductor 33, the resistance 34 in shunt with a condenser 35, therheostat 36 and the 37, the parts of the circuit beconductor ingconnected across the anode and cathode as shown in Fig. 1. Theresistance, inductance and capac ty quantities in this circuit thiscritical value being are preferably so predetermined as torender thecircuit non-inductive, so that changes in this circuit due to changes inthe voltage across the magnetron electrodes will be instantaneously'efifected.

In the preferred construction, the magnitude of the magnetic fieldproduced by the coil 32 is made about equal to the magnitude of thefield producedby the coil 16, the resultant of these fields beingregulated to be equal to the critical value of the magnetron. With thisconstruction it will be seen that half of the magnetic field isproportional to the voltage between the cathode and the anode, and theother half of the magnetic field is maintained constant, this as willpresently appear, producing a total magnetic field which at all times isproportional to the square root of the voltage between the a cathode andanode, making the high tension current passing through the magnetronindependent ofinstantaneous voltage variations between the cathode andanode, which variations are the result of resistance and inductancechanges in the receiver circuits due to such causes, for example, as thechange in frequency of the circuit during the operation thereof,especially when the resistances and inductances .are of very largemagnitudes. That the coils l6 and 32 will produce together a. totalmagnetic field which is at all times proportional to the square root ofthe voltage between the cathode and anode. may be seen from thefollowing example, Assuming a voltage variation' of 4%, as for example achange in voltage across the electrodes from 100 to 104 volts, when themagnetic fields of the coils- 16 and 32 are equal, the coil 16 producesaconstant magnetic field having a value say of 50, and the coil 32 thenhasa value which will change from to 52 so that the total resultantfield varies from 100 to 102; therefore have the following: Rgs ultantfield 100 102 11 f tr a! Volta e c anges mm #1009 104 a change from10.0000 to 10.0019 (5r 1/50th of 1% which change is infinitesimal, theratio thus IBIHZIIIIIIIO constant in all substantial respects. Tius withthese assumed values, the magnetron will not be afi'ecte'd by thevoltage variation, and the sound producing apparatus is rendereddependent only on the mechanical'vibrations.

, Referring now to the modification shown in FigLQ of the drawings,in'which the parts ,are'shown diagrammatically and the magetizing coilsdissociatedfrom the magnetron "tube for'purposes of clarity, the meansfor com ensatin for volta e variations com P g e "prises a circuitconnected in parallel with the receiver 27' without includingthe highthe said circuit includand the conductor 33'.

denser 35', rheostat 36 connected across the receiver 27 by means of theconductor 37', It has been found that the receiver 27' is the maincause'of the instantaneous voltage variations due to the resistance andinductance thereof so that these voltage variations will producecorresponding instantaneous current variations in the coil 32, resultingin corresponding instantaneous field variations. The field roduced bythe coil 32 in this case should be in opposition tothat produced by thecoil 16, the latter coil producing by itself preferably an extinguishingfield pensating' coil 32 having a value such as to and the comkeepconstant the proportion between the resultant field and the square rootof the voltage. As the circuit of the coil 32' is connected directlybetween the two ends where the variations of this voltage occur, it caneasily be regulated b means of the rheostat 36' so as to respon in theright proportionvto these variations. The remaining parts of thearrangement shown in Fig. 2

are similar to those shown in Fig. 1, and are designated by similar andprimed reference characters.

Referring now to Fig. 6 of the drawings, I show a diagrammaticmodification of'the magnetron in which a'full cylindrical anode 12 isemployed in the tube 10, the filament 11 being arranged eccentricallyrelatively to the anode "12, the center of the anode being representedas c, the tube 10 being fitted to a diaphragm 23, with the arrangementsuch that the diaphragm is placed perpendicularly to the center line MNwhich passes through both centers 11' and a.

With this arrangement it will be seen that -11 represents the boundaryof the electron field produced by the desired magnitude of the magneticfield.

The use and'operation of the will in the main be fully apparent 0111 theabove detailed dGSCIiPtlOH- thereof. It will be further apparent thatalthough I have shown my invention applied on a diaparatus phragm orsounding board'directly responsive to sound such as speech to,electrically produce sound proddcing variations in an electric circuit,this applicationof the invention has been given merely byway of example,and that otherapplications will be "obvious to those skilled in the mFor example, the magnetron may be subjected" to vibrations of amechanical vibrating sys-- controlling magnetic means for producing anelectron discharge 'tem such as are employed in phonograph soundregroduction for the transmission of.

speech. t will be further seen that with the provision of the apparatusextremely sensitive and pure transmitter is obtained which in additionis entirely free from unavoidable secondary current changes which occurin known transmitters.

While I have shown my device in the preferred forms, it will be obviousthat many changes and modifications may be made in the structuredisclosed without departing from the spirit of the following claims.

I claim: v H

1. In combination, an electron discharge device having a cathode, ananode an a means for producing an electron discharge [controllingmagnetic field, a circuit connected to the cathode and anode, and meansfor changing the magnitude of said magnetic field proportionate tochanges in the critical valueof the electron discharge device due tovariations in said circuit.

2. In combination, an. electron discharge device having a cathode, ananode and a means for producing an electron discharge field, a receivercircuit connected to the cathode and anode, and means for compensatingforffluctuations in the voltage active across the, cathode and anode due.to variations in said receiver 'circuit.

3. In combination, device having a cathode,

an electron discharge an anode and a controlling magnetic field,avreceiver circuit connected to the cathode and anode, said circuitincluding a source of energy, and means the same relafor maintainingsubstantially tive proportions between the magnitude of the saidmagnetic field and the square root of the voltage active across thecathode and anode.

'4. In combination, an electron discharge device having a cathode, ananode and a means for producing an electron discharge controllingmagnetic field, means for effecting vibrations of the device to producevari ations in the electron stream impinging on the anode, a receivercircuit connected to the cathode and anode, and means for changing themagnitude of said magnetic field proportionate to changes in thecritical value of the electron discharge device due to variations insaid receiver circuit.

5. Incombination, an electron discharge device having a cathode, ananode and a means for producing an electron discharge controllingmagnetic field which is at or about the critical value of the device, areceiver circuit connected to the cathode and anode, and means forchanging the magnitude of said magnetic field proportionate to *5changes in the critical value of the electron described an controllingmagnetic the invention defined in f cuit.

means for producing discharge device due to variations in said receivercircuit.

.6. In combinatiom-an electron discharge device having a cathode,ananode' and a means for producing an electron discharge connected tothe cathode and ano means for changing the magnitude 0% said magneticfield propch'tionate to changes in the critical value of the electrondischarge de and field, a receiver; circuit device due to variations insaid receiver circuit. I

7. An apparatus for producing sound by variations of an electricalcurrent comprising anelement. vibratable in response to sound impulses,vice vibrated thereby, a receiver circuit connected to and controlled bythe electron discharge device, and means for compensating 'forfluctuations in the voltage active across the electrodes of vice due'tovarrtions in said receiver cir- 8. device havmg a cathode, an anode anda means for producing an electron discharge controll ng magnetic field,a receiver circuit an. electron discharge de-- In combination, anelectron discharge the electron discharge deconnected to the cathode andanode, means for producing a second magnetic field cooperating with thefirst magnetic field to produce a resultant at or aboutthe criticalvalue ofthe electron discharge device, and means for changing themagnitude of said resultant magnetic field proportionate to changes inthe critical value of the electron discharge device due to variations insaid receiver circuit. Y 9, In combination, an electron discharge devicehaving a cathode,

an electron discharge controlling magnetic field, a receiver circuitconnected'to the cathode and anode, means for producing a secondmagnetic field cooperating with the first magnetic field to produce aresultant magnetic field, and means for changing the magnitude of saidresultant magnetic changes in the critical value of the electrondischarge device due to variations in the receiver circuit.

10. In combination, an electron discharge device having a cathode, ananode, and a means for producing an electron discharge fieldproportionate to v I field, the said duce changes sultant magnetic",field proportionate to changes the critical value of the magducing a maconnected to t inductive circuit connected to said receiver 7 circuit,the non-inductive circuit includ ng magnetic a"'means for producing asecond.

non-inductive circuit connected to the receiver circuit as in themagnitude of being so to prothe renetron;

p as

- the former and connected to the cathode a means for 1 to changes inthe bration of the same 12; In combination, a magnetron having an anode,a cathode and a means for pro ducing a magnetic field, a receivercircuit and anode, a nonmductive circuit connected to said receivercircuit, the non-inductive circuit including field e ual in magnitude tothe first magnetic eld, the said non-inductive circuit being soconnected to the receiver circuit as to produce changes in the magnitudeof the resultant magnetic field proportionate critical'value of themagnetron; v i 13. An apparatus for producing sound by variation of anelectrical current comprising an electron discharge device having acathode, anjanode, and ameans for producing an electron dischargecontrolling magnetic field, the anode and cathode being eccentricallyarranged relatively to each other and 7 means for effecting the relativemovement of said cathode and anode to produce variations in the electronstream'dischargingfrom impinging on the latter. 14'. An ap aratus forproducing sound by variations 0 an electrical current comprising amagnetron having an anode and a cathode eccentrically arrangedrelatively to each other, and means for effecting the vi to producevariations in producing a second magnetic ode and anode of the electronstream impinging on themagnetron anode.

15; In combination, an electron discharge device having an anode and acathode eccen- .TIIG thereto, and means for producing a on said deviceof a the radius of the field of electrons emanating from the cathode issubstantially equal to the shortest distance betweenthe cathode and theanode.

16. In combinationan electron discharge device having a cylindricalanode and a cathode eccentric thereto, and means for producing amagnetic field active on said device magnetic field active magnitudesuch that of a magnitude such that the radius of the field of electronsemanating from the oath ode is substantially equal to theshortestdistance between-the cathode and the anode.

17. The methodiof compensating for fluctuations in the voltage activeacross the cathan electron discharge de- "vice of the ty e in which theelectron emission is control ecl by a magnetic field, which consistsin'changing the magnitude of the magnetic field proportionately to thechanges in the critical value of the electron discharge device due tosaid voltage fluctuations across the cathode and anode 18 The method ofcompensating for fluctuations in the voltageactive across the oathodeand anode of'an electron discharge device of the ty e in which theelectron emission is controlled by a magnetic field, which consists inmaintaining substantially the same relative nitude of the sad magneticfield and the square root of the voltage active across the cathode andanode. v

Signed at Niagara Falls, in the ,county proportions between the magt ofN iagaraand State of New York this30th day of July, A; D. 1923. p

THEODORE BODDE.

